Subject matter of the present invention are low solvent sol-gel systems, their production and use.
Originally, the sol-gel process has been used to ultimately obtain ceramic masses or glasses from initially solvent compounds via the intermediate stage of a gel. A particular advantage of this process is the production of far more homogenous products as opposed to the classic ceramic methods. In addition, the production of superior coatings can be realized, wherein an alcoholic solution of hydrolysable alcoholates is applied with polyvalent metal ions on a surface and a metallic hydroxyl network is formed as the alcoholic solvent evaporates. This coating, which contains numerous MOH groups is hydrophilic and antistatic. As the temperature rises, the MOH groups react under dehydration to metal oxide groups so that the surfaces become hard and scratch-resistant. Oftentimes, such materials find application as binder materials. Production of stable phases (sols) typically involves the catalytic hydrolysis of alkoxy silanes with acids or bases in aqueous solution up to a certain degree, filling with siliceous sol or other particles, and adjustment with alcohols as solvent to a process-based predetermined solids content. Examples of application for such systems are non-abrasive coatings, corrosion protection, coatings suited to a refractive value, e.g. spectacle glasses or the like.
Some time ago, the use of nanoparticles for the afore-described production of stable phases has provided the basis for a significant development of respective coatings. As a consequence, further functions could be introduced into the systems contained as product, such as, e.g., a better adjustment of the refractive value or IR absorption and even higher abrasion resistances and dirt-repellent characteristics.
DE 198 16 136 A1 discloses a process for the production of sol-gel systems, in which the solvent, typically an alcohol, is removed from the reaction system preferably under reduced pressure. In this way, aqueous or alcoholic sol-gel systems have been produced which were present as single-phase, water-dilutable systems.
The teaching of the DE 198 16 136 A1 is based on the recognition that the extraction of the alcohol is required to develop the reaction, especially of the coating of nanoparticles with organically modified alkoxy silanes such that a system is established that is hydrolysis-stable and condensation-stable, wherein these systems can be used for the afore-mentioned coating purpose. The DE 198 16 136 A1 discloses the removal of alcohol exclusively under vacuum conditions and at temperature of up to 40° C. at the rotary evaporator.